The major goal is to understand the fundamental mechanisms for cellular commitment to mortality. We concentrate on the critical distinction between immortal early embryonic cells and mortal differentiating derivative cells. Our approach is to optimize the use of systematic genomic approaches for profiling gene expression patterns by large-scale cDNA sequencing and cDNA microarray technology with a current cohort of 15,257 genes collected from early mouse embryos. We are particularly focusing on two closely related experimental systems. (1) Preimplantation development - the process of fertilized egg gradually losing its totipotency. In our previous work, we identified many genes that show stage-specific expression patterns during preimplantation mouse development. However, these genes have been identified by EST frequency, which is a relatively inaccurate and far from ideal way to do gene expression profiling. The cDNA microarray-based gene expression profiling will provide more reliable information. To this end, we have been working on large-scale gene expression profiling of each stage of preimplantation mouse development. To start to examine whether these genes identified here might be involved in the immortal/mortal transition process, we are currently analyzing the nature of these genes in greater detail. We are also testing various antisense oligonucleotides to inhibit the function of specific gene in preimplantation mouse embryos. (2) Differentiation of the urogenital system: Germ line cells are often viewed as immortal, because they provide continuity from generation to generation and do not seem to age. To begin the analysis of gene expression regulation involved in germ line-somatic cell interactions, we conducted gene expression profiling by sequencing cell type-specific cDNA libraries that include E13.5 male and female primordial germ cells as well as two stages in the kidney-urogenital developmental axis, E12.5 female mesonephros and newborn ovary. We are currently analyzing genes differentially expressed in these cells, tissues, and organs more in detail.